Farm Forestry New ZealandTechno-economic analysis of posts from specialty wood species and radiata pine
By Peter Hall and Rosie Sargent, August 2021.
Download SWP-T127- (pdf)
Executive summary
The volume of post and pole grade logs cut from New Zealand plantation forests is in the order of 400,000 cubic metres per annum. Some of this material goes to non-post uses and some volume (up to 28%) is lost during processing. The total volume of wooden posts and poles produced is estimated to be around 270,000 to 310,000 cubic metres per annum.
This study is intended to compare the potential for producing posts from durable eucalypt species with the well-established CCA treated wooden post market, as well as posts made from other materials. There are a wide range of non-wooden posts on the market, made from concrete, steel, recycled plastic and hybrids made from a mix of materials. Generally, these non-wooden posts have retail prices that are higher than the CCA treated wooden posts.
The costs of durable eucalypt posts were estimated to be $890 per cubic metre when the costs of growing and processing, including profit margin were included. CCA treated pine posts and non- wood post retail prices were estimated.
| CCA pine | Durable Eucalypt* | Steel | Concrete | Plastic | Wood/plastic | Wood/concrete | |
| Retail price; 1m3 wooden posts or equivalent number of non- wooden posts | $741 | $890 | $1,749 | $2,029 | $1,202 | $1,006 | $1,470 |
*estimated
Non-CCA treated posts have the advantage of being acceptable for use on organic farms and orchards and should be easier to recycle or dispose of after their useful life is over. End of life disposal costs for CCA treated posts are likely to be around $75 per cubic metre.
Given the estimates available on the area of organic farming and horticulture, the potential demand for non-CCA treated posts was calculated. In total there could be a demand for up to 17,000m3 of non-CCA treated wooden post per annum with the bulk of this driven by vineyards, as they have high numbers of posts per hectare and comparatively high breakage / turnover rates. Additionally, the New Zealand wine industry is aiming to achieve zero waste to landfill by 2050 (New Zealand Winegrowers, 2021), which will provide additional demand for non-CCA posts.
Due to the predominance of vineyards in the volume of posts demanded, much of the non-CCA wooden post demand is expected to be in Marlborough, as it has almost 70% of the total national area in vineyards with expansion in recent years being several hundred hectares per annum.
Taking the eucalypt tree crop harvest volumes predicted from a 20-year rotation and the assumed conversion factors likely to be achieved it was estimated that a forest harvest area of 60 ha per annum would be required to meet the post demand from organic growers. This implies a total forest estate dedicated to growing durable eucalypt posts of around 900ha. The Nelson / Marlborough demand is currently around 11 to 12,000 m3 per annum.
Based on this analysis making durable Eucalyptus posts that are cost competitive with non-wood options is possible.
A further consideration is the green-house gas footprint of the various options. Posts made of concrete and steel will inevitably (due to the high energy intensity fossil fuel (coal) based processes used to make them) have a higher GHG footprint than posts made of wood (which are a medium-term store of carbon). The heat in the form of steam used in a post treatment system will largely come from post peelings which are a low carbon fuel. The ecological footprint of plastic posts is less clear, they are made from a waste stream and so reduce volume to landfill but will require heat to melt the plastic prior to it being formed into posts. There is the potential to recycle the plastic posts again should they be damaged whilst in service. There is likely to be some end of life disposal of all posts, regardless of type. However, the LCA of the various routes was not a focus of this analysis but may be of merit at a later stage.
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